India.
Problems with consanguineous marriages.

Around the globe consanguineous marriages have been practised by many societies from time immemorial. It is widely practiced in Asia, North Africa, Switzerland, Middle East, some parts of China, Japan and fishermen communities in Europe and America. One in two rural marriages in Tamil Nadu and Andhra Pradesh are consanguineous.

What type of marriages are consanguineous marriages? When you marry biologically related or blood relatives then it is consanguineous marriage. Most commonly in our part of the world, first cousins — uncle's son marries auntie's daughter or vice versa.

However another type of marriage is where maternal uncle marries his niece (sister's daughter). Theoretical risk of having a genetic defect child is higher in the latter type of marriage than the former. Most of us do not even recognize the pros and cons of such marriages.

While assessing the consequence of consanguineous against non-consanguineous (non-blood related) marriages in health and disease, several scientific studies have shown that consanguinity leads to death of infants before, during or immediately after birth, increased incidence of birth defects, genetic diseases including blinding disorders, blood cancer (acute lymphocytic leukemia), breathing problems for children at birth (apnea), increased susceptibility to disease etc.

Some scientists contradict these studies and state that other biological factors could be accountable for the results and not consanguinity alone.

In our study we showed that consanguinity could increase the incidence of many blinding disorders like retinitis pigmentosa, Leber congenital amaurosis, Lawrence-Moon-Bardet-Biedl syndrome, Stargardt disease, Usher syndrome etc (Consanguinity and Ocular Genetic Diseases in South India: Analysis of a Five-year study. Community Genetics: 2002:5:180-185). Consanguinity could increase the risk of inheriting any one of the 4968 (autosomal recessive) genetic diseases that could affect any part of the body from head to foot.

Some animal studies have shown that inbreeding or consanguinity could enhance longevity. It has been proved beyond doubt that consanguineous marriages farther than second cousins would not result in major genetic diseases.

There are certain misconceptions regarding marriages amongst relatives, marriages between social relatives like wife's brother and husband's sister can get married, where there is no role for blood relationship.

Why do consanguineous marriages result in children with genetic diseases? Due to inheritance parents and children, and brothers and sisters, commonly share 50 per cent of their genetic make-up.

Similarly uncle and niece share 25 per cent and first cousins 12.5 per cent of their inherited genetic material as it originates from a common ancestor. In such situations if there are any `silent' genetic defects, then such errors manifesting as a disease in the child of a consanguineous parents is high.

Whereas, if we marry a person non-consanguineously in a random manner, then for both the partners to share the same `silent' genetic defect is extremely rare.

Hindus in northern India as a practice outlaw the consanguineous marriage by avoiding the same `gothra' or patrilineal relationship between the probable bride and the groom. In some of the western countries including the United States consanguinity closer than the first cousins are considered to be legally incest.

Historically closest consanguineous marriage was performed between brothers and sisters by the Egyptian Pharaohs to preserve the royal blood and interestingly Cleopatra was born out of such marriage. However this disgusting practice has never been duplicated anywhere else in the world.

It is sad to note that many movies in Tamil Nadu and Andhra Pradesh highlight and glorify consanguinity. Evidence suggests that consanguinity does play a negative role in human health. The social benefits of consanguinity should not outweigh the biological damages; many in the community are ignorant about these facts.